Preparation and characterization of dense lanthanum-doped bismuth titanate ceramics

Abstract

In this work, we present an effective way to increase the density of lanthanum-doped bismuth titanate ceramics (Bi4−x La x Ti3O12; BLT). Dense BLT ceramics with formula Bi4−x La x Ti3O12 (when x = 0.25, 0.5, 0.75, 1.0) are prepared by using nanocrystalline powders fabricated by the sol-gel method and high-pressure technique. The thermal decomposition and phase transformation process of the gel precursors are studied by using DTA, infrared spectroscopy (IRS) and X-ray diffraction (XRD). The microstructures of BLT ceramics are investigated by using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The experimental results indicate that the phase compositions of all samples with various La substitutes at 900°C possess the layer-structure of Bi4Ti3O12 (BTO). The green pellets are pressed under 2.5, 3.0, 3.5 and 4.0 GPa, separately. It is found that the density of BLT ceramics is significantly increased due to the decreasing of porosity in the green compacts by the high-pressure process. The samples are sintered at temperatures between 900 and 1100°C and it is found that the optimum sintering temperature is 1100°C. Dense BLT ceramics with 90% of their theoretic density have been achieved from the sample prepared at a sintering temperature of 1100°C for 1.5 h.